Re: Humming sound from LCD

Brian Smithson (
Mon, 15 Jul 1991 10:00:28 -0700

On Jul 15, 1:21am, Hyunsuk Seung wrote:
> Subject: Humming sound from LCD
> Has anyone noticed the humming sound created by the back lighting
> on the LCD panel? I'm just curious if this is a problem only on
> my unit or whether it's normal for an LCD display to behave this
> way. It's noticeable when the room gets quiet.
> --
> H. Seung 4001 Pine St. 2-F
> University of Pennsylvania Philadelphia, PA 19104
>-- End of excerpt from Hyunsuk Seung

It's from the DC-DC converter that powers the display. It's like a
switching power supply, if you're familiar with those. You're probably
hearing some harmonic of the switching frequency resonating in the windings
of a small transformer. I've also noticed that you can hear that humming
sound in a telephone if you have the UltraLite modem hooked up to the same
telephone line.

-Brian Smithson
 Motorola Inc., Computer Group, Commercial Systems Division
 10700 N. De Anza Boulevard, Cupertino, CA 95014 USA, (408)366-4104, {apple | pyramid}!motcsd!brian